A former French paratrooper is hoping to become the first free-falling human to break the sound barrier tomorrow when he jumps from a helium-filled balloon 25 miles above the Canadian plains.

Michel Fournier, 64, while shrugging off concerns about his age, has acknowledged that there are possible dangers – let alone the unknown effects of breaking the sound barrier in free flight.

Backed by a team of scientists and doctors, Fournier has spent two decades and millions of pounds in his bid. Previous attempts have had to be cancelled because of technical and weather problems and Fournier is praying for good conditions.

He will put on a specially modified spacesuit to protect him from solar radiation and temperatures as low as minus 100C and will climb into a pressurised compartment the size of a telephone booth to rise under a helium balloon to 130,000ft.

At that height he will see the blackness of space and the profound curvature of the Earth. There is so little air resistance that it will be like diving into a vacuum – he expects to hit the sound barrier of 769mph in a few seconds. He will accelerate further to reach 1,000mph as he drops through the stratosphere.

If all goes well, he will open his parachute at a height of about 10,000ft. His main concern is to prevent himself going into a spin and blacking out.

“I’ve been training most of my life for this,” Fournier said. “I am ready.”

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